1. Field of the Invention
The present invention relates to a method for transmitting information between at least two transceivers linked together by a bidirectional communication channel, said information being enclosed within at least one frame split into time slots separated from each other by guard intervals having each a predetermined duration, each time slot being allocated either to a first or to a second direction of communication offered by the bidirectional communication channel.
2. Description of the Related Art
The advantages of bidirectional communication channels for transmitting time-splitted frames are currently being assessed for the purpose of defining future generations of wireless telecommunication systems, particularly systems of the TDD type (standing for Time Division Duplex). In such systems, the bidirectional communication channel may for example enable a mobile terminal to send data to a base station in a so-called uplink direction, said base station conversely sending data to said mobile terminal in an opposite, so-called downlink, direction.
According to the known state of the art, the time slots are generally chosen of rather short duration, for example 0.666 milliseconds in a UMTS system compared to a standard frame duration of 10 milliseconds. One of the reasons for such a choice is the aim of obtaining almost invariant channel properties during the time duration of such a slot, i.e. during the time needed for transmitting the data included in said slot. Current theory provides that each slot should systematically include, in addition to its data payload, pilot symbols which are to be analysed by the receiver of said slot in order for said receiver to estimate the current channel properties on the basis of alterations observed with respect to expected pilot symbols. This receiver will thus be able to apply a pre-equalization, i.e. an equalization performed before transmission, to a data signal to be sent back immediately in the reverse direction through the same communication channel. In theory, if the time slots are short enough, the channel will not have varied and the pre-equalization will then almost perfectly compensate for the alterations the channel will cause to this data signal, which should ensure that said data arrive in their original, uncorrupted state and may thus be immediately processed without having to perform a local post-equalization, i.e. a local equalization performed after transmission.
Suppressing the need for local post-equalization is of particular interest when said equalization is to be performed by a mobile terminal whose computing resources are limited by the capacities of its internal processors, as well as by its finite power supply, usually constituted by a battery.
Additionally, pre-equalization is also of interest when performed by a mobile terminal, since it helps fighting adverse channel effects without requiring to raise the transmit power said terminal is to apply to the signal to be transmitted to the base station.
In the known art, a guard interval is usually provided between two successive slots in order to prevent them from interfering with each other. During such a guard interval, no information of any sort is hence to be transmitted. In a cellular telecommunication system, the duration of such a guard interval is determined on the basis of the size of the cell, which indicates the longest possible transmission delay between a mobile terminal and its relevant base station, which determines a highest round trip delay. According to current specifications of future telecommunication systems, cell radiuses may be considered smaller than one kilometer, so that the duration of a guard interval may be chosen equal to 6.7 microseconds.